1. Field of Invention
The present invention relates to a semiconductor structure and its fabrication. More particularly, this invention relates to a pick-up structure for capacitors of DRAM cells and to a DRAM process including the formation of the capacitor pick-up structure.
2. Description of Related Art
There are generally two types of capacitors for DRAM cells, including stacked capacitor and deep-trench (DT) capacitor, wherein the DT capacitor is formed in the substrate and the capacitance thereof can be easily increased by increasing the trench depth, so that much less lateral area is required.
Since the trenches of the trench capacitors are formed quite deep, an N-band is formed quite deep in the substrate to electrically connect the bottom electrodes of all capacitors. To pick up such a deep N-band, in the prior art, multiple ion implantations of different doses and energies are conducted to form a wide deep N-well, and then a contact is formed on the deep N-well as the contact of the N-band.
However, the prior-art method limits the integration degree because the deep N-well requires a certain lateral area even when the memory cell dimension is reduced, and is quite tedious due to the multiple ion implantations. Accordingly, a new pick-up structure for DRAM capacitors is desired to improve the integration degree of DRAM as well as to simplify the DRAM process.